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Forty children are among hundreds of civilians trapped in a chemical plant in Severodonetsk, with the last bridge to the eastern Ukrainian city destroyed by Russian forces.
The city has in recent weeks been the site of intense violence and has become a focal point for Russian President Vladimir Putin’s ambitions to seize enough territory so that he can increase pressure on Kyiv.
Sergiy Gaiday, the Governor of the Luhansk region, said the Azot plant was under heavy bombardment by Russian forces, putting the lives of those trapped inside at risk.
"About 500 civilians remain on the grounds of the Azot plant. Forty of them are children," he said.
The situation is similar to Russia's siege of the Azovstal steel plant in the south-eastern city of Mariupol, where hundreds of fighters and civilians were holed up for weeks with limited food, water and medical supplies.
Ukrainian fighters there surrendered in May, bringing an end to the most brutal siege of the war to date.
Before the invasion, the Azot site in Severodonetsk was one of Europe’s largest chemical plants, producing vast quantities of products such as nitrogen fertilisers and household chemicals.
There are no more routes for people to flee the city after Russian forces destroyed the last bridge linking it to the Ukrainian-held city of Lysychansk on the other side of the Donets River, a Ukrainian official said.
Russian troops are "trying to gain a foothold in the central part of city", the Ukrainian military said on Tuesday as street battles in Severodonetsk continued.
Mr Gaiday said it was impossible to send humanitarian aid to the city.
"It is now fully impossible unfortunately to drive into the city, to deliver something to the city. Evacuation is impossible," he said.
He wrote on the Telegram app that Russia had not yet taken full control of the city and that "a part" remained under Ukrainian control.
Mr Gaiday told Radio Free Europe/Radio Liberty's Ukrainian service that although 70 per cent of the city was in Russian hands, the situation for Ukrainian troops there was "difficult but under control".
Russian troops in the Donbas region were "creating conditions for the development of the offensive on Sloviansk", and an offensive on the towns of Lyman, Yampil and Siversk – all west of Severodonetsk and Lysychansk, the Ukrainian military said.
At least five people were killed on Monday in the Donetsk region, which is controlled by Russian-backed separatists, Russia's Tass news agency reported. Separatist officials say there has been a surge in Ukrainian shelling in recent days.
Kyiv did not immediately comment on the situation.